I wanted to do the big three upgrade in my car....can i do this in Factory batteries and alternator?

It doesn't hurt to do the big 3, and it can be done on any vehicle. You don't 'need' to change the alternator, but factory alternators weren't designed to handle the load of multiple amplifiers. I like capacitors, as they will help stabilize voltage, but a high output alternator is definetly the best way to go. For your particular setup, I don't think you need to change the alternator. I would do the big 3 and run at least a .5 farad capacitor.